From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: kasan, slub: fix more conflicts with CONFIG_SLAB_FREELIST_HARDENED When CONFIG_KASAN_SW_TAGS is enabled, ptr_addr might be tagged. Normally, this doesn't cause any issues, as both set_freepointer() and get_freepointer() are called with a pointer with the same tag. However, there are some issues with CONFIG_SLUB_DEBUG code. For example, when __free_slub() iterates over objects in a cache, it passes untagged pointers to check_object(). check_object() in turns calls get_freepointer() with an untagged pointer, which causes the freepointer to be restored incorrectly. Add kasan_reset_tag to freelist_ptr(). Also add a detailed comment. Link: http://lkml.kernel.org/r/bf858f26ef32eb7bd24c665755b3aee4bc58d0e4.1550103861.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Reported-by: Qian Cai <cai@xxxxxx> Tested-by: Qian Cai <cai@xxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/mm/slub.c~kasan-slub-fix-more-conflicts-with-config_slab_freelist_hardened +++ a/mm/slub.c @@ -249,7 +249,18 @@ static inline void *freelist_ptr(const s unsigned long ptr_addr) { #ifdef CONFIG_SLAB_FREELIST_HARDENED - return (void *)((unsigned long)ptr ^ s->random ^ ptr_addr); + /* + * When CONFIG_KASAN_SW_TAGS is enabled, ptr_addr might be tagged. + * Normally, this doesn't cause any issues, as both set_freepointer() + * and get_freepointer() are called with a pointer with the same tag. + * However, there are some issues with CONFIG_SLUB_DEBUG code. For + * example, when __free_slub() iterates over objects in a cache, it + * passes untagged pointers to check_object(). check_object() in turns + * calls get_freepointer() with an untagged pointer, which causes the + * freepointer to be restored incorrectly. + */ + return (void *)((unsigned long)ptr ^ s->random ^ + (unsigned long)kasan_reset_tag((void *)ptr_addr)); #else return ptr; #endif _
